Bariatric surgery, specifically Roux-en-Y gastric bypass (RYGB), is the most effective and durable treatment for morbid obesity and potentially a viable treatment for type 2 diabetes (T2D). The resolution rate of T2D following RYGB approaches 80% and far surpasses that achieved by medical management alone. The molecular basis for this improvement is not entirely understood. We hypothesize that the altered enterohepatic circulation of bile acids (BA) after RYGB mediates the metabolic improvements that underlie the resolution of T2D after the procedure. In this proposal we will determine how BA contribute to improved lipid and glucose homeostasis, insulin sensitivity and energy expenditure after RYGB. We will apply a novel surgical procedure to diet-induced obese (DIO) mice where bile is diverted from the gallbladder (GB) to the duodenum (GB-D, a sham procedure), the jejunum (GB-J), or ileum (GB-IL). The biliary diversion (BD) procedure permits examination of altered bile flow, similar to that observed after RYGB, independent of alterations in gastrointestinal tract anatomy. Remarkably, the GB-IL procedure, but not GB-D or GB-J, recapitulates many of the beneficial metabolic and physiologic outcomes observed after RYBG. Specific Aim 1 will elucidate the contribution of altered fat absorption, chylomicron generation and clearance in the efficacy of GB-IL or RYGB. Studies in Specific Aim 2 are designed to define the role of membrane-bound BA receptor, TGR5, on glucose homeostasis after RYGB and GB-IL. In Specific Aim 3 we extend our investigations to the nuclear BA receptor, farnesoid x receptor (FXR), investigating the efficacy of RYGB and BD in mice genetically-engineered for intestine- and liver-specific FXR deficiency. The long-term goal of this work is to understand the mechanisms of metabolic improvement after bariatric procedures and to develop technically simple procedures and pharmacologic strategies to treat obesity and its sequelae.